Conventional image devices such as an image forming device or an optical print head comprise a lens plate made from resin such as polycarbonate with plural lenses linearly disposed at predetermined regular Intervals, and a base plate made from resin such as polycarbonate with a number of image arrays linearly disposed. Both plates are secured to a pair of supporting bodies so that each lens corresponds to each image array by way of 1:1. Light emitting elements of respective image arrays are individually lit up by feeding external electric signals to cause light beam from the elements to be focused on an external photo sensitive body through one of the lenses for forming a latent image thereon.
Conventionally, each image array incorporates 64 light emitting elements; in the case of an image forming device capable of forming a 200 DPI resolution Image for B-4 size papers, it includes 32 LED arrays or 2048 light emitting elements. And the number of the light emitting elements increases with the resolution of the device. Each LED array has a common electrode on its bottom surface; the common electrode is adhered to a wiring pattern formed on the upper surface of the base plate, for example, by a conductive resinous adhesive agent such as an epoxy resin and silver powder adhesive, and thus the common electrode is electrically connected to the common electrode wiring pattern. Individual electrodes provided on the upper surface of each LED array are electrically connected to individual electrode wiring pattern formed on the upper surface of the base plate with bonding wires. The pattern on the upper surface of the base plate is connected to an external electric circuit; each light emitting elements of respective LED arrays is driven by an external electric signal.
However, since the total number of individual electrodes of the LED arrays of an image device is several thousands, a very long time and care are needed to the wire bonding, thus resulting in the poor productive efficiency and poor yield. Not only such an image forming device, but an image reading device such as an image sensor using a CCD arrays also contains similar defect.
In order to solve those defects, one of the inventors has already proposed an image formation device comprising plural image arrays disposed between a first substrate, provided with common electrode wiring pattern, and a second substrate provided with Individual electrode wiring pattern, (U.S. patent application No. 08/243,948, now U.S. Pat. No. 5,444,520). The second substrate has a window, and the photo sensitive or light emitting elements of the image arrays face the window, wherein the common electrode of each image array is connected to the common electrode wiring pattern of the first substrate and individual electrodes are connected to the individual electrode wiring pattern of the second substrate by flip chip connection. According to the image device, since individual electrodes are connected to the individual electrode wiring pattern by flip chip connection, several thousands of individual electrodes are precisely and solidly connected all at once. Flip chip connection material is, for example, solder.
Nevertheless, erroneous connection easily occurs in the course of connecting the individual electrodes of the image arrays to the individual electrode wiring pattern of the second substrate by the flip chip connection. This is because there are as many as several thousands of individual electrodes, and yet, each electrode is extremely fine, for example, being 50 .mu.m square in size. Furthermore, the image arrays are sandwiched between the two substrates; the individual electrodes are hardly discernible. As a result, the individual electrodes are often connected to pads that do not correspond to the individual electrode wiring pattern.
Furthermore, with respect to the image device, since the width of the second substrate is about 25 times the width of the image arrays for example, in the course of connecting the second substrate onto the image arrays positioned on the first substrate, the second substrate is apt to tilt itself, if the second substrate tilts itself, the reliability and strength of the flip chip connection will be lower, and crack may be generated in upper surface edges of the image arrays. Furthermore, while the image device being used, if any external force is exerted against the first or second substrate, image arrays easily incur damage such as a fissure or crack.